Aromatic acetates as grinding aids



United States Patent 3,420,686 'AROMATIC ACETATES AS GRINDING AIDS Frank G. Serafin, Peabody, Mass., assiguor to W. R. Grace & Co., Cambridge, Mass., a corporation of Connecticut No Drawing. Filed Feb. 17, 1965, Ser. No. 433,504

US. Cl. 106-90 15 Claims Int. Cl. C04b 7/54; C04b 7/58 ABSTRACT OF THE DISCLOSURE Aromatic acetates '(e.g., hen l acetate a d. -nitromadam set inhibitors in minerals ang gement (e.g., portland cement). M

This invention relates to grinding minerals and more particularly to the use of an additive for improving the grinding efficiency and pack set characteristics of minerals.

Inthe processing of minerals, either in the unprocessed or semiprocessed state, a grinding operation is generally necessary to reduce the particular mineralto a relatively small particle size. It is desirable in this grinding step to have as efiicient an operation as possible, that is, to reduce the particular mineral to the desired particle size at a relatively rapid rate.

Cleavage of the particles during grinding of the minerals exposes fresh or nascent surfaces which have high energies due probably to the breaking of ionic bonds. The surface forces of the ground particles persist for some time after grinding and lead to compaction or pack set and/or poor fluidity if they are not reduced. Mineral particles when compacted by vibration, e.g., when transported in a hopper car, often become semirigid and will not flow until considerable mechanical eiiort has been applied to break up the compaction. On the other hand, undue reduction or the complete absence of surface forces is undesirable because the finely ground mineral becomes excessively fluid.

A grinding aid is a material which assists in grinding of minerals, either by increasing the rate of production or by increasing the fineness of the particles at the same rate of production without having adverse effects onany of the properties of the ground product.

The term pack set as used herein is intended to refer to the agglomeration or adhesion of particles by, e.g., storing or transporting in bulk. Adhesion results from surface forces, the majority of which are created during the grinding of the minerals. Pack set index is a relative term which numerically indicates how prone a particular material is to start flowing after it is stored or transported in bulk. Pack set index ratio is the relative pack set index of the untreated sample compared to the treated sample. This ratio is used to permit comparison between different samples of the mineral.

Pack set index is determined in the following manner: 100 grams of the mineral is placed in a 250 milliliter Erlenmeyer flask set on top of a variable vibrator. The flask containing a mineral is vibrated 15 seconds after which time it is removed from the vibrator and fed into a jig with the axis of the flask lying horizontally. The flask is then rotated about its axis until the mineral which is compacted on the bottom of the flask collapses. The flask is twisted by turning at 180 angles at approximately 100 twists per minute. The number of 180 twists required for the mineral sample to collapse establishes the pack set index. Thus, the greater the energy requirement to break up the bed, the higher will be the pack set index.

A novel additive has now been found which will function as a grinding aid and a pack set inhibitor for min- Examines erals. The novel additive of the present invention is an aromatic ester of an alkanoic acid. The term aromatic ester of an alkanoic acid, as used herein, is intended to include substituted aromatic esters of analkanoic acid. Preferably, the ester is of a lower alkanoic acid, e.g., esters of acetic, propionic and butyric acids. The additive may be represented by the formula:

wherein Y is an aromatic group, e.g., phenyl or naphthyl; X is a substituent on the aromatic ring and may be nitro; halogen, preferably chloro; alkyl, preferably a 1 to 5 carbon alkyl, more preferably methyl; aryl; hydroxyl; amino; and alkoxy, preferably a 1 to 5 carbon alkoxy group; n is 0, 1, 2, or 3; and R is an alkyl group, preferably a 2 to 4 carbon alkyl group. In a preferred embodiment, X is nitro or methyl, n is 1, Y is phenyl, and R-is ethyl. A particularly preferred additive is phenyl acetate.

As illustrative of additives within the scope of the invention, mention may be made of the following:

Phenyl propionate Phenyl butyrate l ,2-dimethylphenyl acetate 1,4-dimethylphenyl acetate 2,4-dimethylphenyl acetate p-Nitrophenyl acetate o-Nitrophenyl acetate Methylphenyl acetate a-Naphthyl acetate p-Naphthyl acetate a-Naphthyl propionate fl-Naphthyl propionate Z-hydroxylnaphthyl acetate p-Chlorophenyl acetate The additive is interground with the mineral in the grinding mill to provide increased grinding efficiency as well as other advantageous result, e.g., inhibiting pack set of bulk stored materials. It has also been found that the novel additive of the present invention also serves to provide fluidity to the ground minerals when they are being transported by conveying systems, particularly by pneumatic air systems. i

The term mineral as used herein is intended to refer to naturally occurring inorganic minerals, such as phosphate rock, partially processed minerals such as concentrated iron ore, and mixtures of minerals such as cement clinker or ceramics. As examples of such minerals which can be processed with the additive of the present invention, mention may be made of beryllium oxide, limestone, gypsum, clays, and bauxite.

The grinding aids of the present invention are particularly preferred for use with cement, particularly portland cement.

Portland cement represents a class of hydraulic cements and is comprised essentially of two calcium silicates and a lesser amount of calcium aluminate. These cements are-produced by heating an intimate mixture of finely divided calcareous material (limestone) and, argillaceous material (clay) to fusion to form a clinker. The clinker is ground with the addition of about 2% gypsum, or some other form of calcium sulfate, to obtain the desired setting qualities in the finished cement. 'It is to the clinker that the novel additive of this invention is preferably added to increase grinding efficiency and to inhibit subsequent pack set in the finished cement.

The additives of the present invention are employed in either dry or liquid form. For convenience, the additive is in a water solution to permit accurate metering into the mineral stream. In instances where the additive is not very soluble in water, it can be utilized in liquid form by emulsifying it with a suitable wetting agent, e.g., sodium dodecyl benzene sulfonate. The addition is accomplished either prior to the grinding or the additive is introduced into the grinding mill simultaneously with the mineral. If the additive is employed merely for reduction of pack set and fluidizing purposes, it is added at any convenient point in the processing.

The additive of the present invention is employed preferably as the sole grinding aid, but is should be understood that it can also be employed with a mixture of one or more grinding aids or in admixture with cement additives other than grinding aids.

The additive is employed effectively over a relatively wide range. The preferred range is about 0.001 to 1%. and more preferably about 0.005 to about 0.04% based on the weight of the mineral, i.e., weight of additive solids based on weight of mineral solids (herein referred to as solids on solids). In a particularly preferred embodiment about 0.025% of the additive based on the weight of the mineral is employed. The higher levels are employed if grinding to a relatively high surface area, and the amount of additive used is limited only by the'desired surface area and fluidity of the finished product.

In Table 1 the effectiveness of phenyl acetate as a grinding aid is reported along with data on pack set characteristics. The data was collected on a type I portland cement ground in a laboratory steel ball mill for 4400 revolutions at 210 F.

TABLE 1 Blaine surface Pack set index In Table 2 ASTM C185 air entrainment data is reported on cements interground with phenyl acetate. In all the compositions tested, the water/cement ratio was 0.70. The data shows that the use of phenyl acetate as a grinding aid does not result in a greater degree of air entrainment than the blank.

In Table 3 the ASTM C109 compressive strength data is shown of mortars prepared from cements which were interground with the novel grinding aid of the present invention. In all compositions tested the water/cement ratio was 0.49. For comparative purposes mortars prepared from cements which were ground without an additive but which had similar Blaine surface areas are included in the table. The cements which contain the additive were ground for 4400 mill revolutions at 210 F. The blanks were ground at 210 F. for a time sufficient to produce the reported part cle size.

TABLE 3 Amount of Blaine Compressive strength, p.s.i. additive (persurface area,

cent solid on sq. em./g. l-day 7-day 28-day solid) 3, 020 785 3, 025 4, 575 3, 020 798 3, 075 3,950 3, 035 935 3, 400 4, 675 3, 070 765 a, 000 4, 900 3, 880 3, 375 4, 875 3, 970 3, 125 4,428 a, 250 920 3, 5, 150 3, 320 99s 3, 500 5, 162 3, 420 972 3, 450 4, 850 3, 430 1, 055 3,875 5, 412 3, 560 1,040 3, 812 5, 412 3, 560 945 3, 725 5, 275 3,560 1, use 4, 138 5,800 3, 560 1, 142 3, 975 6, 125 3, 560 1, 252 4, 100 5, 238

Table 3 shows that the 1-day compressive strengths of the blanks are generally somewhat higher than those of the cements containing the additive of this invention. However, except at very low levels of additives, the 28- day compressive strengths of the cements containing the additives are substantially greater than those of the cements with no additives but which had similar Blaine surface areas.

The following table illustrates the increase in grinding efliciency achieved with p-nitrophenyl acetate. Type 1 portland cement was ground in a laboratory steel ball mill for 5408 revolutions at 210 F.

TABLE 4 Amount of additive Blaine surface (percent solid on solid): area (cmF/ g.) Blank 3140 In order to illustrate the advantageous properties of the novel additive of this invention, typical properties of cement interground with phenyl acetate and other grinding aids are compared below in Table 5. All additives were used at the 0.0330% solids on solids level, and the grinding conditions were the same for all the cements.

From the above table it will be seen that the additive of this invention is significantly superior in grinding efficiency to the other acetate grinding aids (3.3% better than methyl acetate) and the commercial grinding aid (8.4% better) which is an acetate type. The above table also shows that cement interground with phenyl acetate has superior pack set inhibition characteristics. The compressive strength characteristic is also found to be superior in cements containing the grinding aid of this invention, with the exception of the 28-day strength of the sample with the methyl acetate. However, it will be noted that the 1- and 7-day strengths are higher for phenyl acetatecontaining samples than for methyl acetate-containing samples.

While the additive of the present invention is described primarily in terms of grinding cement clinker, satisfactory results are obtained when the additive is utilized in grinding other minerals.

What is claimed is:

1. A composition consisting essentially of a solid material selected from the group consisting of minerals and cement and, intimately admixed therewith, an ester having the structural formula:

wherein Y is an aromatic group; X is an aromatic ring substituent selected from the group consisting of nitro, halogen, aryl, hydroxyl, amino, and alkyl and alkoxy of 1 to 5 carbon atoms; n is -3, and R is an alkyl group of 1 to 4 carbon atoms, the amount of said ester present being sufiicient to increase grinding efficiency when said composition is ground in a grinding mill.

2. A composition as defined in claim 1 wherein said ester is used at a level of about 0.001 to 1% by weight based on the weight of said solid material.

3. A composition as defined in claim 1 wherein said ester is a phenyl acetate.

4. A composition as defined in claim 3 wherein said phenyl acetate is present at a level of about'0.025% based on the weight of said solid material.

5. A composition as defined in claim 1 wherein said solid material is a hydraulic cement.

6. The method which comprises intergrinding a solid material selected from the group consisting of minerals and cement with an ester having the structural formula:

wherein Y is an aromatic group; X is an aromatic ring substituent selected from the group consisting of nitro, halogen, aryl, hydroxyl, amino, and alkyl and alkoxy of 1 to 5 carbon atoms; n is 0-3, and R is an alkyl group of 1-4 carbon atoms, the amount of said ester present being suflicient to increase grinding efficiency.

7. The method as defined in claim 6 wherein said ester is added to the solid material prior to introducing the solid material into the grinding zone.

8. The method as defined in claim 6 wherein said ester 6 is present at a level of about 0.001 to 1% by weight based on the weight of said solid material.

9. The method as defined in claim 6 wherein said ester is phenyl acetate.

10.A method as defined in claim 6 wherein said ester is p-nitro-phenyl acetate.

11. The method as defined in claim 6 wherein said solid material is portland cement.

' 12. A composition consisting essentially of a solid material selected from the group consisting of minerals and cement and, intimately admixed therewith, an ester selected from the group consisting of substituted and unsubstituted phenyl and naphthyl esters of alkanoic acids containing up to 4 carbon atoms, the amount of said ester present being about 0.001 to 1% by weight based on the weight of said solid material.

13. The composition of claim 12 wherein said solid material is portland cement.

14. The method which comprises intergrinding a solid material selected from the group consisting of minerals and cement with about 0.001 to 1% by weight, based on the weight of said solid material of an ester selected from the group consisting of substituted and unsubstituted.

phenyl and naphthyl esters of alkanoic acids containing up to 4 carbon atoms.

15. A composition consisting essentially of portland cement and, intimately admixed therewith, 0.001 to 1% by weight, based on the weight of said cement, of phenyl acetate.

References Cited UNITED STATES PATENTS 2,360,518 10/1944 Scripture 106-9 0 3,068,110 12/1962 Fagerholt l0690 JAMES E. POER, Primary Examiner.

U.S. Cl. X.R. 

